1. Field of the Invention
This invention relates to analog circuits and, more particularly, to operational amplifiers.
2. Description of the Related Art
One of the most widely used electronic devices in the electronics industry is the operational amplifier, or ‘op-amp’. Operational amplifiers are very efficient and versatile devices that are used in various applications to meet design requirements for signal conditioning, special transfer functions, analog instrumentation, and analog computation, among others.
For analog design, operational amplifiers are classified as either class A, class B, class AB, or class C. Class A amplifiers typically have low distortion, but they have poor efficiency. Class B and class C amplifiers have excellent efficiency, but they create a large amount of distortion. Class AB amplifiers, which are generally designed to have two output transistors in a push-pull arrangement, achieve a compromise between efficiency and distortion.
One technique for designing class AB operations amplifiers is to use translinear loops to control the current in the output stage of the amplifier. This solution is generally not very accurate and also requires extra circuitry, which makes it rather complex to design. Another drawback with the above-mentioned method is the stability of the amplifier. The added circuitry usually introduces more poles and hence de-stabilizes the circuit.